Protected metal and process of making it



. July 15 1924. 1,501,887

' F. M. CRAPO PROTECTED METAL AND PROCESS OF MAKING; IT

"Filed Dec. 10 v 1923 VIII/111111711]; I 4

Patented July 15, 1924.

UNITED STATES tsetse? PATENT caries.

FREDERICK M. CRAPO, CF MUNCIE, INDIANA, ASSIGNOR TO INDIANA STEEL & WIRE COMPANY, OF MUNCIE, INDIANA, A CORPORATION OF INDIANA.

PROTECTED METAL AND PROCESS OF iMAKIN G IT.

Application filed December 10, 1923. Serial No. 679,650.

T all whom it may concern:

Be it known that I, FREDERICK M. CRAro, a citizen of the United States, residing at Muncie, in the county of Delaware and State of Indiana, have invented a new and useful Protected Metal and Process of Making It, of which the following is a specification.

The primary object of my invention is -to improve the zinc-coating of iron and steel articles, and especially of iron and steel wire. More specifi'cally,'such primary object is to produce a. zinc-coated article, especially iron or steel wire, the coating of which will adhere firmly and will not peel or flake off even when subjected to sharp bends or twists, as for example upon wrapping a wire around its own diameter; and especially to accomplish all this effectively with iron and low-carbon steel, with which such result-s can not be obtained by ordinary galvanizing.

It 'is a further object to get this improved zinc-coating without adversely affecting the mechanical and electrical properties, such as tensile strength, elongation, and electrical resistivity.

A further object is to simplify, cheapen, and shorten the process of cleaning and (or) annealing at any stage of the manufacture ofiron and steel wire. This cleaning and (or) annealing may be used as a preparation for-zinc-coating; or as a mere independent opcration, without relation to immediate zinc-coating, or to any zinc coating at all.

i till another object is to get a more satisfactory and lasting zinc-coating with a smaller amount of zinc.

In accomplishing these results, from the standpoint of zinc-coating, I pass the ironbase article, such as iron or low-carbon steel wire, advantageously after it" has reached the gage at which it is to be coated and preferably in a continuous operation in the case of Wire, through a suitable surfacetreating, advantageously in a bath, to prepare the surface for the application of the zinc-coating; and subsequently apply the zinc-coating. I am not fully certain of the action of this surface-treating bath, but the bath I have used with best success contains carbonizing material, such as a commercial cyanide mixture of any suitable proportions, maintained in molten condition at a temperature advantageously between 1200 and 1300 F. I believe that this produces a superficial carbonizing action on the iron-base (or ferrous metal) body, and soproduces a relatively high-carbon surface condition. In any event, it hassome action on the surface of the iron-base body so that when the coating of zinc is subsequently applied, as upon passing wire so treated through a bath of molten zinc, better adherence of the coating is obtained, and the coating has superior mechanical properties. It is my belief that the superior nature of the zinc coating which I obtain is accounted for primarily by the superficial carbonizing action before mentioned on the ironbase body, but it is also possible that it may be due to the improved condition of the surface of the iron-base body or to these things in combination.

Further, by passing the wire through the bath referred to, 1 find that I, obtain not only this surface-treating effect, probably a very thin surface carbonizing, but also obtain at least two additional and very valu able effects. In the first place, I find that I obtain a very effective annealing of the wire, following its various passages through the dies up to that point; so that it is possible completely to eliminate the usual annealing furnace which heretofore it has always been considered necessary to provide after the wire has been drawn down to a certain size. In the second place, I find that the bath of molten salts, in addition to the surface-treating and the annealing effects, produces a most effective cleaning action; so that it is possible to eliminate or reduce the period of immersion in the acid bath or baths through which the annealed wire is usually passed for cleaning just prior to entering the molten zinc, though I prefer to retain a short acid bath, or to provide a zinc chloride or other' bath, just before the molten zinc, in order to get the desired fluxing action.

Thus by the immersion of the iron-base article in the aforesaid bath of molten salts I obtain a very effective chemical heat-- treating, which has many advantages. By the term chemical heat-trcating I mean the production in the iron-base (or ferrousmetal) body of both a permeative addition by chemical change and a heat-treatment; such for example as annealing and superficial carbonization, both of which occur in my bath of molten salts.

By avoiding or reducing the period of immersion in acid I practically eliminate loss of iron, for there is substantially no such loss in the chemical heat-treating. Further, I believe .I avoid the occlusion of hydrogen in the surface of the iron base body, such as occurs in acid treati'nent. This may contribute to the production of the surface condition which causes better adherence of the ZlIlC coating when the latter is subsequently applied.

I prefer to treat the wire in this bath of molten salts after it has passed through all the dies necessary to reduce it to the desired gage, to get the cleaning and annealing action just prior to coating. IIowever, so far as producing a non-peeling zinc coating is concerned, it is not essential that this surface treatment be at this point in the process. It may be at any earlier point in the process, though then it may be necessary to produce a. second annealing and a cleaning just prior to zinc-coating, on account of intervening actions on the wire. \Vhen such a second annealing and cleaning is done, it may be either by passing the wire through a second and similar bath ofmolten salts, in accordance with my invention, or may be in the old way of passing the Wire through an annealing furnace and then through an acid bath for cleaning. In other words, the surface effect which my bath of molten salts produces will follow the wire all the way through the series of dies or through any part thereof which may be desired.

In consequence, I have found it possible even to use this annealing and cleaning method on thes original rods, of about onequarter inch diameter, with which the wiredrawer starts in the manufacture of wire, and to obtain a most effective cleaning thereby. Thissi'nakes it possible to eliminate the usual long and somewhat complicated method of cleaning rods prior to drawing. Further, by avoiding the acid pickling which forms part of the usual preparatory process, I largely eliminate the loss of iron and the occlusion of hydrogen already referred to, and also lessen or eliminate the tendency to become brittle. This preliminary cleaning and treatment in the bath of molten salts may be supplemented by one or more subsequent annealings and cleanings, whether in the same or some other manner; but whether or not there is any other subsequent treatment by passing through a bath of molten salts, this preparatory treatment produces on the surface some effect, probably carbonizing, which persists throughout all the subsequent operations, and makes it possible to apply a better zinc coating, if desired, when the final gage has been reached.

Further, I have found that this treatment of the surface of the wire in the bath of molten salts produces some sort of preserving effect, even if there is no subsequent zinc-coating. In other words, a wire which has been treated by passing it through this bath of molten salts is found to be less susceptible to corrosion than the same wire which has not been so treated. The chemically heat-treated wire has a very dense and smooth surface, which even without further protection (as by zinc-coating) persists under adverse conditions.

In addition, this treatment of the surface of the wire by passing it through the bath of molten salts is found to have no detrimental elfect on-the electrical and mechani cal properties of the wire; so that all the advantages of a low-carbon content are retained, and also there are added advantages.

In using this bath of molten salts, I have found it possible to vary the composition of the bath very greatly. I believe the bath should contain some carbonizing material, mixed with other things servin mainly as fillers or dilnents. A most advantageous mixture which I have used contains 60% sodium cyanide, 20% sodium carbonate, and 20% sodium chloride. Further, the temper ature of the bath may be varied quite considerably, and I have found the process very effective with temperatures ranging from about 1200 F. to about 1300 F.

The bath of molten salts may be covered with a thin layer of coke, if desired, to lessen exposure to the atmosphere and consequent heat loss due to radiation. This layer of coke also serves partly as a wipe for the wire as it leaves the bath, thus effecting a reduction in the loss of salts.

The bath is preferably so arranged that the wire remains in it only for a short time. No period of immersion which I have tried has proven too short, even down to 7 or 8 seconds; but I prefer an immersion of about 15 seconds, to obtain a more complete an nealing and a desirable cleaning,bas well as the desired surface" treatment, and greater pern'iissible tolerance in the period of immersion and the temperature of the bath.

In the accompanying drawings, I have illustrated apparatus for practicing my proccss and producing my improved product: Fig. '1 is a longitudinal sectional View show ing diagrammatically an apparatus for surfacetreating, annealing, and cleaning a wire by chemically heat-treating it after it has been drawn to the deslred gage, and for zinccoating it following such chemical heat treating. all in continuous operation; and Fig. 2 is a longitudinal sectional view showing dingrammatically an apparatus for surface-treat ing and cleaning rods in a continuous process in preparation for wire-drawing.

lxel'erring tirst to the apparatus shown in Fig. 1:-

The iron-base wire 10, of iron or low-car-- bon steel, is presumed to have been passed previously through the desired sizing dies.

until it has reached the gage at which it is desired to zinc-coat it. Then it is passed through a tank 11, containing my bath of molten carbmiizing salts then. with sullicient inter al for some. cooling, through a bath 1?. of water for removing any adhering salts: then through a fluxing bath 13 of any suit.- able flux. such as of hydrochloric acid or zinc chloride; and then through a bath 14 of molten zinc, in which the wire takes its zinc coating. From the zinc-coating bath l-l, of molten zinc. the wire passes to the winding reel 15. All this is in a continuous process. with the wire continuously moving in the direction of the arrows.

lVhile the zinc coating may be applied in various ways. the way I prefer to apply it. especially to wire, is by passing the wire through a bath of molten Zinc. The zinccoating bath 14 is advantageously maintained at about 840 F. to 900 F, in any convenient way; though that temperature may be varied at the judgment of the operator.

If desired, and usually it is desirable, a

i hot plate 10 may intervene between the fluxing bath 13 and the molten-zinc bath 14. so that the wire will be dry when it enters the molten zinc.

The chemically heat-treating bath 11 contains the molten carbonizing salts 17, above referred to, preferably covered by a coke layer 18. These salts 17 are maintained at a temperature somewhat above their melting point, advantageously between 1200 F. and 1300 F., as by a fire 19 below the bath 11. For carrying 011' fumes, a hood 20' is preferably provided over the bath 11. This bath 11 serves to give the desired surface treatment, which it is the fundamental object of my invention to obtain. It also acts to produce the desired annealing and cleaning; so that the usual annealing furnace may be dispensed with, and so that no acid bath is needed for-cleaning, although a short acid bath 15 may be used for fluxing.

Referring now to the apparatus shown in Fig. 2

The rod 10' from which the series of drawing operations starts is passed through a tank 11, containing my bath of molten carbonizing salts; then through a bath 12 of Water for removing any adhering salts; and then to the winding reel 15. All this is in continuous operation. The molten salts 17' in the bath 11' produce a chemical heat- I treatment on the rod 10, and effectively clean it; so that from the reel 15' the rod is ready to go to the drawing dies. The salts 17 in the bath 11 are. maintained in molten condition by a fire 19 below; may be covered by a layer of coke 18', if desired, though that is not necessary; and preferably have a hood 20 above them for carrying off any fumes If desired, in order to lessen the time of immersion in the bath 11' of molten salts, the rods 10 may be passed through a bath 25 of molten lead just previous to entering the bath 11.. The molten lead in the bath 25, when that bath is used, serves to heat the rod. so that less rise in tem erature of the rod will be necessary in t e bath of molten salts, and the. period of immersion in the molten salts may be reduced. The bath 25 of molten lead is thus merely a preliminary heating means for the rod or wire, and may be used as such preliminary when ever desired in practicing my invention; but it is merely a convenient preliminary, and is not essential. It is not shown in Fig. 1.

I claim as my invention 1. A, zinc-coated iron or steel article, comprising an iron-base body which is of relatively low carbon content in the interior but has a relatively high-carbon surface condition, and a coating of zinc upon and adhering to said high-carbon surface.

2. A zinc-coated iron or steel article, comprising a low-carbon iron-base body which has been treated in a bath of molten carbonizing salts, and a coating of zinc upon and adhering to the surface of such treated ironbase body.

3. A chemically heat-treated iron or low carbon steel article, and a zinc coating upon and adhering to such article.

4. Zinc-coated iron or steel wire, comprising an iron or steel core, and a zinc coating thereupon and adhering thereto; the iron or steel core being of relatively low carbon content in the interior, but. having a relatively high carbon content at the surface where it adjoins the zinc coating.

5. Zinc-coated iron or steel wire, comprising a low-carbon iron-hase core which has been treated in a bath of molten car-. bonizing salts, and a coating of zinc upon and adhering to the surface of such treated core.

6. Chemically heat-treated iron 'or lowcarbon steel wire, and a zinc coating upon and adhering to such wire.

, 7 The process of zinc-coating an iron or low-carbon steel article, which consists in immersing the article in a carbonizing bath of molten salts, and subsequently immersing it in a bath of molten zinc.

8. The. process of zinc-coating an iron or 10. The process set forth in, claim 7, with the addition that the article is immersed in a fluxing material between its inimersions in the two molten baths.

11. The process set forth in claim 7, with the addition that the article is washed and then treated with a flux between its immersion in the two molten baths.

12. The process of zinc-coating an iron or low-carbon steel article, comprising chemically heat-treating said article, including carbonizing the surface of said article, and subsequently zinccoating such. article.

13. The process of zinc-coating an iron or low-carbon steel. article, comprising chemically heat-treating the surface of said article, and subsequently zinc-coating such article. I

14. The process of zinc-coating an iron or low-carbon steel article, comprising so chemicall heat-treating the surface of said article t at it promotes the bonding thereto of a zinc coating, and subsequently applying such Zinc coating.

15. The process of zinc-coating an iron or steel article, comprisingannealing and cleaning such article and producing a nermeative addition by chemical change. in the surface of such article in a single operation, and subsequently applying a zinc coating to such article.

16. The process of Zinc-coating an iron or steel article of such composition that ordinary galvanizing thereof produces a coating which peels and cracks on bending or twisting, comprising chemically heattreating such article to produce a sinrface-condition thereof, which on coating with zinc will take a substantially non-peeling coating; and subsequently applying such zinc coating.

17. The process of making zinccoated iron or low-carbon steel wire, which consists in drawing the wire to a desired gage, subsequently passing it through a carbonizing bath of molten salts to produce a carbonizing treatment of the surface of the wire and also to produce a cleaning and annealing of the wire, and subsequently passing the wire through a bath of molten zinc.

18. The process of making zinc-coated iron or low-carbon steel wire, which consists in drawing the wire to a desired gage, subsequently passing it through a bath of molten salts to produce such a chemical heattreatment of the surface of the wire that iron or low-carbon steel wire,

amass? the adherence of a zinc coating to such surface will be increased, and to produce a cleaning and annealing of the wire, and subsequently passing the wire through a bath of molten zinc.

19. The process of making zinc-coated which consists in drawing the wire to a desired gage and carbonizing the surface of the wire, and subsequently passing the wire through a bath of molten zinc.

20. The process of making zinc-coated iron or steel wire, comprising drawing the wire to a desired gage; and at any desired stage in the manufacture of the wire pass ing the wire through a molten bath of carbonizing salts to producean annealing and a cleaning and also a superficial change in the wire and subsequently both to the drawing operation and to the passage of the wire through. the bath of molten salts passing such wire through a bath of molten zinc to apply thereon a zinc coatin 21. The process of making zinc-coated iron or steel wire, comprising drawing the wire to a desired gage; and at any desired stage in the manufacture of the wire chemi cally heat-treating the wire; and subsequently both to the drawing and the heat-treating operations applying a zinc coating to such wire.

22. The process set forth in claim 21, with the addition that the treating and Zinc-coating operations are continuous.

23. The process of zinc-coating iron or steel wire, comprising producing such a chemically different surface-condition of the wire by permcative addition by passing it continuously through a bath of molten salts that it has greater adherence for a zinc coating subsequently applied, while maintaining the other parts of such wire than the surface thereof without substantial chemical change,

and subsequently applying a zinc coating to such wire.

24. The process of zinc-coating iron or steel wire, comprising producing such a change in the surface of the wire by chemically heat-treating the wire that its surface has greater adherence for a zinc coating subsequently applied, while maintaining the other parts of such wire than the surface thereof without substantial chemical change, and subsequently applyinga zinc coating to such wire.

The process of making a zinc-coated iron or steel article, comprising making an iron-base body with a relatively high carbon content at its surface and a relatively low carbon content in its interior, and applying a zinc coating to the surface of such iron-base body.

26. The process iron or steel wire,

of making a zinc-coated comprising making an iron-base wire with a relatively high caruid medium, and subsequently zinc-coating bon content at its surface and a relatively said article. to low carbon content in its interior, and ap- In Witness whereof, I have hereunto set plying a zinc coating to the surface of such my hand at \Vashington, D. (3., this 10th 5 iron-base Wire. day of December, A. I). one thousand nine 27. The process of zinc-coating an iron or hundred and twenty three.

low-carbon steel article, comprising chemically heat-treating said article in a hot liq- FREDERICK M. CRAPO. 

